#define trigPin 9
#define echoPin 10
#define buzzerPin A0

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);

  distance = duration * 0.034 / 2;

  if (distance < 100) {
    tone(buzzerPin, 1000);
    delay(1000);
    
  }

  Serial.print("Distance: ");
  Serial.println(distance);
  delay(500);
}